The present invention relates generally to apparatus for sharpening knives of a cutting reel. More particularly, the present invention concerns a sharpening device which is automatically operated to perform both grinding and indexing functions on the cutting reel.
In the past, various approaches have been used to the sharpen helical knives of a cutting reel. For example, the knives have been individually removed from the cutting reel for sharpening and then replaced. This procedure is time-consuming and generally unsatisfactory for cutting reels used in agricultural equipment in which the cutting edge of the reel is subject to long use and rapid wear. To overcome this problem, partially automated sharpening devices have been mounted on the equipment carrying the cutting reel so as to permit the individual knives to be sharpened without removing the cutting reel or its knives from the equipment. While these sharpening devices have taken various forms, one useful form is disclosed in U.S. Pat. No. Re. 28,200, issued Oct. 15, 1974 to Witt et al.
In this particular prior art device, a carriage is mounted for translation axially with respect to the cutting reel. The cutting reel itself is partially rotated as the grinding device translates on its carriage. This partial rotation of the cutter reel is effected in order to permit the grinding device to uniformly sharpen the edge of a helical cutting knife.
The Witt et al patent has an indexing device to automatically advance the cutter reel and present a subsequent knife after one knife has been sharpened. The particular indexing device, however, is a mechanically complex apparatus which includes a plurality of cams, detents, springs, levers, and mechanical elements which are actuated as the cutting reel is rotated during the grinding operation.
Such indexing devices are difficult and expensive to manufacture due to the multiplicity of parts required. A more significant problem occurs with use of the known indexing devices: as the elements move relative to one another wear develops on the abutting surfaces of the elements which cause after a substantial period of time inaccuracy in the operation of the indexing device. Because of the complexity of and the number of parts, it is difficult to adjust the indexing mechanism so as to accommodate the inevitable wear. It will, however, from a consideration of the importance of the position of the knife relative to the grinding device be apparent that inaccuracies and increased tolerances as a result of mechanical wear may cause such a mechanical indexing device to be unsuited for continued sharpening operations. Moreover, with the mechanical interrelation between the grinding and the indexing operations, it is possible for the grinding operation to become jammed while the indexing operation proceeds. In this event, substantial damage to the cutter knives may occur if they are advanced prior to completion of a sharpening cycle.
It will thus be seen that one of the substantial problems with fully automating the grinding and indexing operation of a sharpening unit for a cutting reel is the problem of separating the grinding operation from the indexing operation so as to avoid potential problems such as the knife damage discussed above.
Another problem with automation of the sharpening unit is the cumulative effect of tolerances in a plurality of mechanical elements. More particularly, the tolerances can permit sufficient lost motion or slack in the system that the timing of the indexing operation may get out of synchronization resulting in damage to the cutter knives. Obviously a damaged knife must be replaced causing loss of operating time and undesirable expense.
It will thus be apparent that the need continues to exist for a sharpening unit for a cutting reel which is capable of automated sharpening and indexing operations.